1. Field of the Invention
The present invention relates to modifiers for use in thermoplastic polyamide compositions that have improved ductility and toughness and to processes for preparing such compositions; specifically, the modifiers of the present invention have better flow and easier dispersibility than previously known materials during compounding with polyamides.
2. Description of Related Art
Thermoplastic polyamides are a class of materials that possess a good balance of properties, e.g., excellent mechanical characteristics, high heat resistance, and good durability, that make them useful as structural materials. On the other hand, they are known to be deficient in impact resistance, notch sensitivity, and moisture resistance. One route to improving impact resistance is by blending the polyamide with another polymer. Unfortunately, it has often been found that such blends provide their own set of problems, e.g., immiscibility between the polyamide and the modifying polymer, which can bring about poor adhesion between the two, leading to weak areas at their interface that result in mechanical failure.
It is difficult to obtain a good dispersion of a combination of a polar polymer, such as a polyamide, with a non-polar polymer, such as a polyolefin. It is known that the addition of a graft or block copolymer of similar chemical structure to the blend components can improve the quality of the dispersion. These copolymers, generally referred to as compatibilizers, are often added as a third component to the blend. Maleic anhydride grafted polypropylene has been suggested as a compatibilizer for polypropylene/nylon blends by Ide et al., J. Appl. Polym. Sci., 18:963 (1974). The compatibilization of polyethylene/polyamide blends with maleic anhydride grafted polypropylene has been reported by Chen et al., Polym. Engng. Sci., 28:69 (1988). These and similar blends have been studied and the results reported by Park et al., Eur. Polym. J. 26(2):131-136 (1990).
A compatibilizing agent is a material that, on a molecular scale, has particular regions that are compatible with each of the incompatible constituent polymers. Such compatibilizing agents typically surround one polymeric phase providing a chemical and/or physical bridge to the other polymeric phase. Insofar as portions of the compatibilizing agent are compatible with each of the constituent polymers, the bonding between the two incompatible polymeric phases is effectively enhanced through this intermediate compatibilizing phase. Such a system of incompatible polymers coupled by a compatibilizing agent results in a material that advantageously combines the more desirable properties of the constituent polymers.
A method of reclaiming mixed immiscible polymers by employing a compatibilizing agent has been described by Lindsey et al. J. Appl. Polymer Sci. 26:1-8 (1981). The system studied was a high density polyethylene (HDPE) and is polystyrene (PS) and a styrene-ethylene-butene-1-styrene (SEBS) copolymer (a linear triblock copolymer) as the compatibilizing agent. These ternary blends exhibited a considerable improvement in the balance of mechanical properties over a binary blend of high density polyethylene and polystyrene.
U.K. Patent Number 998,439 discloses a thermoplastic composition comprising a mixture of 50 to 99 percent linear polyamide and 1 to 50 percent of olefin copolymer particles, the olefin copolymer containing from 0.1 to 10 mole percent of acid groups.
U.S. Pat. No. 3,668,274 teaches improved impact strength of polycarbonamides modified with (A) a first elastomer phase of copolymers or terpolymers and (B) a final rigid phase thermoplastic stage containing amine-reactive moieties, preferably carboxylic acid groups.
U.S. Pat. No. 3,845,163 discloses blends of 60 to 85 percent by weight polyamide and an acid-containing olefin polymer in which the acid is derived from an .alpha.,.beta.-ethylenically unsaturated carboxylic acid and in which at least 10 percent of the acid groups has been neutralized with metal ions.
U.S. Pat. Nos. 3,388,186 and 3,465,059 disclose polyamide compositions that possess high impact strength with some values in excess of 10 foot pounds per inch. The disclosed compositions are graft copolymers prepared from an ethylene containing polymer.
U.S. Pat. No. 4,174,358 discloses toughened multiphase thermoplastic compositions consisting essentially of one phase containing 60 to 99 percent by weight of a polyamide matrix resin of number average molecular weight of at least 5,000 and 1 to 40 percent by weight of at least one other phase containing particles of at least one polymer that is adhered to the polyamide and has a particle size in the range of 0.01 to 3.0 microns and a tensile modulus in the range of 1.0 to 20,000 psi, wherein the ratio of the tensile modulus of the polyamide matrix to the tensile modulus of polymer is greater than 10 to 1.
U.S. Pat. No. 4,427,828 and WO83/00492 disclose blends of thermoplastic polyamide with a modified block copolymer to increase the impact strength of the polyamide.
U.S. Pat. No. 4,647,509 discloses a multilayer thermoformable packaging material comprising a first layer of (a) a vinylidene chloride polymer, (b) an incompatible polymer, e.g., polyesters and nylons, and (c) a compatibilizing agent, and a second layer of (a) a blend of an olefin polymer, a styrenic polymer, and a compatibilizing polymer, and (b) scrap material produced from the first and second layers. The compatibilizing polymers for the second layer are preferably block copolymers of olefins and styrene, such as copolymers of styrene-butadiene, styrene-butadiene-styrene, styrene-isoprene, etc.
U.S. Pat. No. 4,657,970 describes polymer compositions comprising at least one thermoplastic polymer including polyamides, thermoplastic polyesters, thermoplastic polyurethanes, vinyl alcohol polymers, etc., and at least one modified block copolymer of a monovinyl-substituted aromatic hydrocarbon polymer block A and at least one olefin compound polymer block B, to which has been grafted at least one molecular unit containing at least one member selected from a carboxylic acid group and groups derived therefrom. The modified copolymers and compositions are said to have excellent impact resistance, adhesion, paint adhesion, weatherability, resistance to aging, transparency, etc.
U.S. Pat. No. 4,795,782 describes a polymer blend--said to exhibit improved impact resistance--comprising a polyamide, a functionalized polyolefin, and a functionalized elastomer. The functionalized polyolefins are obtained by reacting a polyolefin with an unsaturated mono- or polycarboxylic acid or derivative thereof. Suitable unsaturated mono- or polycarboxylic acids include maleic anhydride, maleic acid, fumaric acid, etc. The functionalized elastomers described are generally functionalized selectively hydrogenated block copolymers of conjugated dienes and vinyl aromatic compounds. The block copolymers are functionalized by grafting the copolymers with a mono- or polycarboxylic acid compound, such as maleic anhydride, maleic acid, fumaric acid, etc. Other monomers that are utilized for introducing the functionality include vinyl monomers, such as acrylamide, acrylonitrile, monovinyl aromatic compounds (e.g., styrene), vinyl esters, vinyl ethers, etc.
U.S. Pat. No. 5,278,231 describes blended polymer compositions said to have improved impact resistance comprising:
(I) from about 1 percent to about 97 percent by weight of at least one alpha-olefin polymer; PA1 (II) from about 1 percent to about 97 percent by weight of at least one polyamide; PA1 (III) from about 1 percent to about 97 percent by weight of at least one polymer of a vinyl aromatic hydrocarbon; PA1 (IV) an effective amount of a mixture of two or more compatibilizing agents selected from the group consisting of PA1 (I) from about 1 percent to about 98 percent by weight of at least one olefin polymer; PA1 (II) from about 1 percent to about 98 percent by weight of at least one polyamide; PA1 (III) an effective amount of a compatibilizing agent which comprises at least one terpolymer of an alpha-olefin, at least one acrylic ester, and an alpha, beta-olefinically unsaturated dicarboxylic acid reagent, or a glycidyl acrylate; and PA1 (IV) from 0 to about 25 percent by weight of at least one auxiliary compatibilizing agent being a member selected from the group consisting of: PA1 (A) an elastomeric olefin copolymer; and PA1 (B) a resinous olefin homopolymer or copolymer PA1 wherein at least one of (A) and (B) is maleated; and PA1 wherein the melt flow index of the resulting composition measured at 230.degree. C. and 2.16 kg weight is at least 3 g per 10 minutes. PA1 (A) an elastomeric olefin copolymer; and PA1 (B) a resinous olefin homopolymer or copolymer PA1 wherein at least one of (A) and (B) is maleated; and PA1 wherein the melt flow index of the resulting composition measured at 230.degree. C. and 2.16 kg weight is at least 3 g per 10 minutes. PA1 (A) an elastomeric olefin copolymer; and PA1 (B) a resinous olefin homopolymer or copolymer PA1 wherein at least one of (A) and (B) is maleated; and PA1 wherein the melt flow index of the resulting composition measured at 230.degree. C. and 2.16 kg weight is at least 3 g per 10 minutes. PA1 (A) an elastomeric olefin copolymer; and PA1 (B) a resinous olefin homopolymer or copolymer PA1 wherein at least one of (A) and (B) is maleated; and PA1 wherein the melt flow index of the resulting composition measured at 230.degree. C. and 2.16 kg weight is at least 3 g per 10 minutes. PA1 suitable lubricants and mold release agents such as stearic acid, stearic alcohol, and stearamides, in a concentration up to 1.0 percent based on the weight of the composition; PA1 organic dyes such as nigrosine, etc.; PA1 pigments such as titanium dioxide, cadmium sulfide, cadmium sulfide selenide, phthalocyanines, ultramarine blue, carbon black, etc.; PA1 fibrous and particulate fillers and reinforcements such as carbon fibers, glass fibers, amorphous silica, asbestos, calcium silicate, aluminum silicate, magnesium carbonate, kaolin, chalk, powdered quartz, mica, feldspar, etc., in a concentration up to 50 percent based on the weight of the composition; PA1 nucleating agents such as talc, calcium fluoride, sodium phenyl phosphinate, alumina, and finely divided polytetrafluoroethylene, etc.; and PA1 plasticizers such as dioctyl phthalate, dibenzyl phthalate, butyl benzyl phthalate, hydrocarbon oils, N-normal butyl benzene sulfonamide, ortho and para toluene ethyl sulfonamide, etc., in a concentration up to about 20 percent based on the weight of the composition. The colorants (dyes and pigments) can be present in an amount of up to about 5.0 percent by weight, based on the weight of the composition.
(a) at least one selectively hydrogenated block copolymer of a vinyl aromatic hydrocarbon and a conjugated diene; PA2 (b) at least one selectively hydrogenated block copolymer of a vinyl aromatic hydrocarbon and a conjugated diene to which has been grafted an alpha,beta-olefinically unsaturated monocarboxylic or dicarboxylic acid reagent; and PA2 (c) at least one terpolymer of an alpha-olefin, at least one acrylic ester, and an alpha,beta-olefinically unsaturated dicarboxylic acid reagent, or a glycidyl acrylate. PA2 (a) at least one selectively hydrogenated block copolymer of a vinyl aromatic hydrocarbon and a conjugated diene to which has been grafted an alpha,beta-olefinically unsaturated carboxylic acid reagent; PA2 (b) at least one polymer which is the product of the reaction of an alpha-olefin polymer and an alpha,beta-olefinically unsaturated carboxylic acid reagent; and PA2 (c) a mixture of (III) and (IVa) and/or (IVb) reacted in the presence of a radical initiator;
U.S. Pat. No. 5,317,059 describes polymer compositions comprising:
provided that when the blended polymer contains one or more of the auxiliary compatibilizing agents (IVa) or (IVb), the blended polymer is free of other polymers of vinyl aromatic hydrocarbons.
Thus, it is seen that the materials heretofore disclosed in the art for modification of polyamides and their blends are primarily maleated elastomers (e.g., EPDM) or maleated polyolefins that are used in improving the compatibility of blends of nylon with polyolefins.
The elastomeric materials, however, suffer from the inherent deficiency of insufficient flow during compounding with the polyamides. This deficiency results from the higher viscosity of the elastomer as compared to the polyamide phase at processing temperatures. The olefinic modifiers have sufficient flow but are not very efficient tougheners for nylon because of their lack of elastomeric character and lack of ductility to absorb impact forces, especially at low temperature.